The present invention relates to foundry and tooling processes and methods.
It is known to form castings such as engine cylinder heads by various foundry techniques in which cores of different shapes are placed within a mold to form voids, such as, for example, water jacket passages and gas ports. In the past, this has required the forming, handling and assembling of numerous cores. A comparatively large number of cores and considerable assembly labor are used in the fabrication of assemblies of this type.
Moreover, conventional core arrangements may require subassembly and pasting or gluing of one or more of the cores together. Such core assemblies are subject to some breakage due to handling, and whenever cores are glued together there are numerous instances in which molten metal flows between the cores and forms fins. When these fins protrude into water jacket passages, they must be removed as they would tend to restrict circulation and interfere with the proper operation of the engine.
Also, in commercial foundries, it is not uncommon for glueing to be performed in such a manner that relatively large amounts of glue remain in hidden or inaccessible areas of the assembled cores. This excess glue acts much as a core would, leaving a void and causing surface imperfections or holes which can necessitate scrapping of the cast piece.
Further disadvantages of conventional core arrangements may include the need for using a large base or positioning core to hold the water jacket cores and port cores in place during core assembly and during pouring.
Another problem associated with conventional cylinder head coring assemblies lies in the need to design the port walls with relatively thick sections in order to allow for proper assembly of the port cores. These thicker than necessary sections have an adverse effect on efficient operation and cooling of the cylinder head.
The majority of the above-described problems were alleviated by the core assembly and method of casting described in U.S. Pat. No. 4,093,018, issued to Trumbauer on June 6, 1978. The patent discloses a casting method wherein a first core is fabricated which has an irregular outer surface, a destructible cellular plastic material is molded around said first core, a second core is molded in an encompassing relation around said plastic layer, with the core assembly then being placed in a mold cavity into which molten metal is introduced. The molten metal destroys the plastic layer and forms the casting.
The search has continued for improved casting methods, particularly in those methods utilizing cellular plastic materials. The presence of a plastic material during casting may result in defects since the destruction of the plastic material with molten metal results in the production of gaseous byproducts which may not always be completely vented from the assembly during the casting process, thus contaminating the molten metal. Defects in the core materials themselves may also be hidden by the plastic layer and would not, therefore, be detected or corrected prior to the initiation of the casting process.